The singer's campaign, #Allin4PR, is raising money to continue support for Puerto Rico one year after Hurricane Maria

Helping Puerto Rico has now become a family affair for Ricky Martin.

One year after Hurricane Maria ravaged the island, the singer, who was born in San Juan, is selling t-shirts featuring a flag of Puerto Rico drawn by his 10-year-old twin sons, Matteo and Valentino, to continue to raise money for victims and communities. “This campaign has been so beautiful,” Martin, 46, tells PEOPLE. “It started with my kids — they wanted to do something to help. So they hand-colored the flags, which became the t-shirt design worn by artists and fans from all over the world.”

The shirts, available until Nov. 30 at, have been worn by celebrities including Will Smith, Carrie Underwood, Sean Penn and Lin-Manuel Miranda. “Everyone joined together to help our island heal,” Martin adds. “It’s been an incredible collaboration.”

The singer’s campaign, #Allin4PR, was launched in September, the week of the one-year anniversary of Hurricane Maria.

“This was stronger than me,” he posted on Instagram. “I couldn’t wait another day. It’s one year later, and we’re STILL #AllIn4PR. The death toll was high after Hurricane Maria, but the spirit of the people of Puerto Rico is UNBREAKABLE. We are resilient. And as we continue to reshape hearts and reclaim hope, we still need your help.”

Martin, who was recently featured in PEOPLE’s Sexiest Man Alive issue, insists giving back is the ultimate reward. “If I couldn’t do something in the arts, I would do something in philanthropy,” said the singer, who is married to Jwan Yosef. “I’m all about helping people feel good and making the world a better place.”

Funds from the T-shirts, which cost $24.99, will be used by the Ricky Martin Foundation to continue to rebuild homes and support communities in Puerto Rico. “We’re grateful to everyone who has worn our flag over their heart in order to help us rebuild homes, reshape lives and empower communities,” Martin says. “We hope you’ll get your t-shirt and join our cause.”